1. Field of the Invention
The present invention relates to a liquid recording head which ejects liquid, and a method of manufacturing the liquid recording head. In addition, the present invention preferably relates to an ink jet head which ejects ink, and a method of manufacturing the ink jet head.
2. Description of the Related Art
Conventionally, there has been known a side shooter type ink jet head which ejects ink toward an upper region of an ejection energy generating element. This type of ink jet head is usually manufactured by bonding an ink jet chip constituted of a substrate to a head substrate having an ink introduction port.
When an ink jet chip is manufactured, a silicon substrate is usually used. There is one in which an ejection energy generating element, an ink flow path, and a nozzle for ejecting ink are formed on a surface of a silicon substrate, and an ink supply port is formed to penetrate from a back surface to a front surface of the substrate. The ink is supplied from the back surface of the substrate to the nozzle on the front surface of the substrate via the ink supply port penetrating the substrate from the back surface.
As a method of forming the ink supply port penetrating the silicon substrate from the back surface to the front surface, for example, there is a method of using anisotropic etching of silicon. This etching method utilizes a difference of etching rate with respect to a crystal orientation of silicon so that a desired shape is obtained.
It is known that, when this anisotropic etching is performed, a thermal oxide film is formed on the back surface of the silicon substrate as an etching mask. The thermal oxide film has high resistance to a strong alkaline solution, which is an etchant, and is therefore suitable for a mask material for the anisotropic etching. Further, the thermal oxide film is also superior in resistance to ink, and hence the thermal oxide film also functions as an ink protective layer of a silicon substrate to be exposed to the ink.
An ink jet chip in which an ink supply port is formed by anisotropic etching is bonded to a head substrate having an ink introduction port by using an adhesive or the like.
However, when this bonding with an adhesive is performed in a state in which the thermal oxide film as the ink protective layer is left on the back surface of the ink jet chip, high adhesive strength cannot be obtained in some cases. It is because the surface of the thermal oxide film has a small number of functional groups for a chemical bonding with the adhesive.
As a method of avoiding this, Japanese Patent Application Laid-Open No. 2009-208383 describes a method in which members are bonded with an adhesive after the ink protective layer having low adhesive strength is removed only from the adhesion site. The silicon substrate of the site from which the ink protective layer is removed becomes a silicon natural oxide film having a plenty of functional groups. Therefore, high adhesive strength can be obtained between the back surface of the silicon substrate and the head substrate when the bonding with an adhesive is performed.
In this way, with the silicon natural oxide film as the adhesive surface, high adhesive strength can be obtained. However, the silicon natural oxide film which is an adhesiveness improving film has low resistance to ink although it provides high adhesive strength for an adhesive. Recent inks frequently contain an alkali component, and so the silicon natural oxide film may be dissolved in the alkali component to some extent. When the ink in which silicon is dissolved is supplied to the nozzle for ejecting ink, and when the ejection energy generating element for generating heat is used, silicon may be deposited on the ejection energy generating element so that a desired ejection pressure cannot be obtained, or the deposited silicon may block the nozzle.
As a method of avoiding such a problem, for example, there is a method in which the silicon natural oxide film is completely covered with an adhesive for bonding the ink jet chip to the head substrate so that the silicon natural oxide film is not exposed to the ink. However, depending on assembly accuracy when the ink jet chip is bonded to the head substrate or dimension accuracy of each component, it may be difficult to completely cover the natural oxide film. In addition, there is a method of preparing an ink not to contain an alkali component, but possible ink formulations may be narrowed.